The penetration of anti-infectives into the central nervous system

The Blood-Brain Barrier and Pharmacokinetic/Pharmacodynamic Optimization of Antibiotics for the Treatment of Central Nervous System Infections in Adults

Bacterial central nervous system (CNS) infections are serious and carry significant morbidity and mortality. They encompass many syndromes, the most common being meningitis, which may occur spontaneously or as a consequence of neurosurgical procedures. Many classes of antimicrobials are in clinical use for therapy of CNS infections, some with established roles and indications, others with experimental reporting based on case studies or small series. This review delves into the specifics of the commonly utilized antibacterial agents, updating their therapeutic use in CNS infections from the pharmacokinetic and pharmacodynamic perspectives, with a focus on the optimization of dosing and route of administration that have been described to achieve good clinical outcomes. We also provide a concise synopsis regarding the most focused, clinically relevant information as pertains to each class and subclass of antimicrobial therapeutics. CNS infection morbidity and mortality remain high, and aggressive management is critical in ensuring favorable patient outcomes while averting toxicity and upholding patient safety.

Delirium Associations with Antibiotics: A Pharmacovigilance Study of the FDA Adverse Event Reporting System (FAERS)

Background

Ertapenem, cefepime, imipenem, ofloxacin, ceftazidime, clarithromycin, cefaclor, levofloxacin, linezolid, moxifloxacin, azithromycin, piperacillin–tazobactam, trimethoprim–sulfamethoxazole, metronidazole, ciprofloxacin, and cefuroxime are known to be associated with delirium. Other antibiotics may also lead to delirium, but no study has systemically compared delirium associations for many available antibiotics.

Objective

The objective of this study was to evaluate the association between delirium and antibiotics using the FDA Adverse Event Reporting System (FAERS).

Methods

FAERS reports from January 1, 2004 to December 31, 2018 were included in the study. Reporting odds ratios (RORs) and corresponding 95% confidence intervals (95% CI) for the association between antibiotics and delirium were calculated. An association was considered to be statistically significant when the lower limit of the 95% CI was greater than 1.0.

Results

A total of 10,015,622 reports (including 16,982 delirium reports) were considered, after inclusion criteria were applied. Statistically significant delirium RORs (95% CI) for antibiotics were: ertapenem 21.07 (16.38–27.10), cefepime 9.8 (6.37–15.09), imipenem 9.68 (6.75–13.89), ofloxacin 7.73 (4.00–14.92), ceftazidime 6.09 (2.73–13.62), clarithromycin 5.34 (4.37–6.53), cefaclor 5.32 (1.71–16.58), ampicillin–sulbactam 4.49 (2.13–9.45), levofloxacin 4.47 (3.88–5.16), linezolid 4.33 (3.28–5.72), moxifloxacin 3.51 (2.81–4.38), azithromycin 2.76 (2.09–3.64), piperacillin–tazobactam 2.41 (1.47–3.93), trimethoprim–sulfamethoxazole 2.36 (1.61–3.47), metronidazole 1.85 (1.31–2.60), ciprofloxacin 1.83 (1.44–2.33), and cefuroxime 1.81 (1.03–3.20).

Conclusion

This study found statistically significant increased risk of reporting delirium with ertapenem, cefepime, imipenem, ofloxacin, ceftazidime, clarithromycin, cefaclor, ampicillin–sulbactam, levofloxacin, linezolid, moxifloxacin, azithromycin, piperacillin–tazobactam, trimethoprim–sulfamethoxazole, metronidazole, ciprofloxacin, and cefuroxime.

Lemierre's syndrome: A forgotten and re-emerging infection

Lemierre's syndrome, also known as post-anginal septicemia or necrobacillosis, is characterized by bacteremia, internal jugular vein thrombophlebitis, and metastatic septic emboli secondary to acute pharyngeal infections. Modern physicians have "forgotten" this disease. The most common causative agent of Lemierre's syndrome is Fusobacterium necrophorum, followed by Fusobacterium nucleatum and anaerobic bacteria such as streptococci, staphylococci, and Klebsiella pneumoniae. The causative focus mostly originated from pharyngitis or tonsillitis, accounting for over 85% of the cases of Lemierre's syndrome. Pneumonia or pleural empyema is the most common metastatic infection in Lemierre's syndrome. Antimicrobial therapy should be prescribed for 3-6 weeks. The treatment regimens include metronidazole and β-lactam antibiotics. In recent years, the antibiotic stewardship program has resulted in decreased antibiotic prescription for upper respiratory tract infections. The incidence of Lemierre's syndrome has increased over the past decade. F. necrophorum is an underestimated cause of acute pharyngitis or tonsillitis. A high index of suspicion is required for the differential diagnosis of acute tonsillopharyngitis with persistent neck pain and septic syndrome.

Atypical Presentation of Lemierre's Syndrome Causing Septic Shock and Acute Respiratory Distress Syndrome

Lemierre's disease is a rare but life-threatening condition characterized by an oropharyngeal infection complicating with thrombophlebitis of the internal jugular vein and disseminated abscesses. We are presenting a case of a young female who initially presented with fevers, chills, sore throat, and swollen neck later developed progressively worsening shortness of breath along with sudden onset pleuritic chest pain. She then developed progressively worsening acute hypoxic respiratory failure requiring intubation and mechanical ventilation. Interval chest X-ray showed worsening bilateral effusions. She also developed septic shock requiring pressors. Blood culture showed Fusobacterium, and antibiotics were changed accordingly following which there was a clinical improvement. The diagnosis of Lemierre's syndrome was then established based on her presenting age and bilateral pulmonary empyema in the setting of septicemia with Fusobacterium.

Central Nervous System Infections in the Critically Ill

Central nervous system (CNS) infections are frequently encountered in the intensive care unit setting and are a significant source of morbidity and mortality. The constantly changing trends in microbial resistance, as well as the pharmacokinetic difficulties in providing effective concentrations of antimicrobials at the site of infection represent a unique challenge to clinicians. Achievement of a successful outcome in patientswith CNS infections is reliant on eradication of the offending pathogen and management of any neurologic complications. This requires an anatomic and physiologic understanding of the different types of CNS infection, diagnostic strategies, associated complications, causative organisms, and the principles that govern drug distribution into the CNS. This article serves as a review of the epidemiology, pathophysiology, diagnosis, and treatment options for a variety of CNS infections, with a focus on those commonly encountered in an intensive care setting.

The Role of Endoscopic Lavage in Recalcitrant Multidrug-Resistant Gram-Negative Ventriculitis Among Neurosurgical Patients

INTRODUCTION

Ventriculitis is a serious infection associated with high mortality even when both intravenous (IV) and intrathecal (IT) antibiotics are administered. Poor outcome in patients with ventriculitis indicates the need to be more aggressive in our attempts to expeditiously eradicate the infection. The purpose of this study was to evaluate the role of endoscopic lavage (EL) in patients with severe purulent ventriculitis, unresponsive to IV and IT antibiotics.

METHODS

All consecutive patients with severe ventriculitis caused by multidrug-resistant gram-negative bacteria, undergoing EL after failure of prolonged courses of IV and IT antibiotics, were included in the study. The outcome in all these patients was otherwise expected to be uniformly dismal.

RESULTS

There were 5 males and 2 females. The age range was one month to 45 years. All patients had frank intraventricular pus. Acinetobacter baumannii was the most common organism grown in cultures. Two patients had multiple bacterial growth in cerebrospinal fluid cultures. The duration of pre-EL IV/IT antibiotics ranged from 3 to 8 weeks. Microbiological cure was achieved in all (7/7) and clinical cure in 86% of patients (6/7). One patient died despite achieving cerebrospinal fluid sterilization 3 months later as a result of progressive white matter edema.

CONCLUSIONS

The addition of IT antibiotics has resulted in improved outcome in patients with ventriculitis; however, some patients continue to be unresponsive to antibiotics. EL can play a complementary role in eradicating such recalcitrant infections. EL should be considered in any patient with ventriculitis, if infection persists even after ∼7-10 days of IVand IT antibiotics.

Imperfect drug penetration leads to spatial monotherapy and rapid evolution of multidrug resistance

Infections with rapidly evolving pathogens are often treated using combinations of drugs with different mechanisms of action. One of the major goal of combination therapy is to reduce the risk of drug resistance emerging during a patient's treatment. Although this strategy generally has significant benefits over monotherapy, it may also select for multidrug-resistant strains, particularly during long-term treatment for chronic infections. Infections with these strains present an important clinical and public health problem. Complicating this issue, for many antimicrobial treatment regimes, individual drugs have imperfect penetration throughout the body, so there may be regions where only one drug reaches an effective concentration. Here we propose that mismatched drug coverage can greatly speed up the evolution of multidrug resistance by allowing mutations to accumulate in a stepwise fashion. We develop a mathematical model of within-host pathogen evolution under spatially heterogeneous drug coverage and demonstrate that even very small single-drug compartments lead to dramatically higher resistance risk. We find that it is often better to use drug combinations with matched penetration profiles, although there may be a trade-off between preventing eventual treatment failure due to resistance in this way and temporarily reducing pathogen levels systemically. Our results show that drugs with the most extensive distribution are likely to be the most vulnerable to resistance. We conclude that optimal combination treatments should be designed to prevent this spatial effective monotherapy. These results are widely applicable to diverse microbial infections including viruses, bacteria, and parasites.

Neurotoxic effects of AZT on developing and adult neurogenesis

Azidothymidine (AZT) is a synthetic, chain-terminating nucleoside analog used to treat HIV-1 infection. While AZT is not actively transported across the blood brain barrier, it does accumulate at high levels in cerebrospinal fluid, and subsequently diffuses into the overlying parenchyma. Due to the close anatomical proximity of the neurogenic niches to the ventricular system, we hypothesize that diffusion from CSF exposes neural stem/progenitor cells and their progeny to biologically relevant levels of AZT sufficient to perturb normal cell functions. We employed in vitro and in vivo models of mouse neurogenesis in order to assess the effects of AZT on developing and adult neurogenesis. Using in vitro assays we show that AZT reduces the population expansion potential of neural stem/progenitor cells by inducing senescence. Additionally, in a model of in vitro neurogenesis AZT severely attenuates neuroblast production. These effects are mirrored in vivo by clinically-relevant animal models. We show that in utero AZT exposure perturbs both population expansion and neurogenesis among neural stem/progenitor cells. Additionally, a short-term AZT regimen in adult mice suppresses subependymal zone neurogenesis. These data reveal novel negative effects of AZT on neural stem cell biology. Given that the sequelae of HIV infection often include neurologic deficits—subsumed under AIDS Dementia Complex (Brew, 1999)—it is important to determine to what extent AZT negatively affects neurological function in ways that contribute to, or exacerbate, ADC in order to avoid attributing iatrogenic drug effects to the underlying disease process, and thereby skewing the risk/benefit analysis of AZT therapy.

HIV reservoir dynamics in the face of highly active antiretroviral therapy

Upon discontinuation of highly active antiretroviral therapy (HAART), human immunodeficiency virus (HIV)-infected individuals experience a brisk rebound in blood plasma viremia due to the exodus of HIV from various body reservoirs. Assessment of HIV dynamics during HAART and following treatment discontinuation is essential to better understand HIV persistence. Here we will first provide a brief overview of the molecular mechanisms involved in HIV reservoir formation and persistence. After a summary of HAART-mediated HIV decay within peripheral blood, we discuss findings from clinical studies examining the effects of HAART initiation and interruption on HIV reservoir dynamics in major anatomical compartments, including lymph nodes and spleen, gut associated lymphoid tissue, reproductive organs, the central nervous system, and the lungs. Features contributing to these reservoirs as distinct compartments, including anatomical features, the presence of drug transporters, and the effect of co-infection, are also discussed.

Antiviral effects of artesunate on JC polyomavirus replication in COS-7 cells

The human JC polyomavirus (JCPyV) causes the fatal demyelinating disease progressive multifocal leukoencephalopathy (PML). A growing number of patients with induced or acquired immunosuppression are at risk for infection, and no effective antiviral therapy is presently available. The widely used antimalarial drug artesunate has shown broad antiviral activity in vitro but limited clinical success. The aim of this study was to investigate the effect of artesunate on JCPyV replication in vitro. The permissivity for JCPyV MAD-4 was first compared in four cell lines, and the monkey kidney cell line COS-7 was selected. Artesunate caused a concentration-dependent decrease in the extracellular JCPyV DNA load 96 h postinfection, with a 50% effective concentration (EC50) of 2.9 μM. This effect correlated with a decreased expression of capsid protein VP1 and a reduced release of infectious viral progeny. For concentrations of <20 μM, transient reductions in cellular DNA replication and proliferation were seen, while for higher concentrations, some cytotoxicity was detected. A selective index of 16.6 was found when cytotoxicity was calculated based on cellular DNA replication in the mock-infected cells, but interestingly, cellular DNA replication in the JCPyV-infected cells was more strongly affected. In conclusion, artesunate is efficacious in inhibiting JCPyV replication at micromolar concentrations, which are achievable in plasma. The inhibition at EC50 probably reflects an effect on cellular proteins and involves transient cytostatic effects. Our results, together with the favorable distribution of the active metabolite dihydroartemisinin to the central nervous system, suggest a potential use for artesunate in patients with PML.

[Tissue penetration of antibiotics. Does the treatment reach the target site?]

BACKGROUND

For critically ill patients, infections still imply a major challenge for the treating physician. One key factor of successful treatment is sufficient exposure of the employed antimicrobial agent at the site of infection. In most cases, this is the interstitial space of the infected organ or a body cavity; much rarer vital bacteria are located within body cells.

METHODS

Different methods for assessment of tissue pharmacokinetics of antimicrobial agents in the human body are described, including tissue biopsy, bronchoalveolar lavage and microdialysis, and their implication on interpretation of obtained data are discussed. Tissue pharmacokinetics of the hydrophilic beta-lactam meropenem and the lipophilic fluoroquinolone levofloxacin are compared.

RESULTS

Differences in pharmacokinetics between plasma and tissue, healthy volunteers and critically ill patients but also between data obtained in the same organ by different methods are discussed.

CONCLUSION

In order to use pharmacokinetic data to optimize the treatment of critically ill patients, critical appraisal of the causative pathogen, the location of the infection, and the source of the used pharmacokinetic data is necessary.

Therapy for neurocysticercosis

Therapy for neurocysticercosis has advanced during the last 20 years with the advent of albendazole (Zentel) and praziquantel (Cysticide). Albendazole is the current medication of choice for the treatment of neurocysticercosis and is recommended for symptomatic patients with multiple viable cysts in the brain parenchyma. Albendazole may also be useful in extraparenchymal cysticercosis, especially in the subarachnoid racemose form, when complete surgical resection of the cysts is usually impracticable. Currently, there is an intense debate over the value and safety of anticysticercal therapy. Causes for failure of anticysticercal therapy include high inter-individual variability in plasma concentration of albendazole sulfoxide and the complex interactions of several drugs with the albendazole metabolite. Furthermore, albendazole sulfoxide is an enantiomeric mixture of (+)- and (-)-albendazole sulfoxide with accumulation of the (+)-enantiomer in the cerebrospinal fluid. However, the question over which enantiomer is effective against cysticerci remains to be clarified.

Lemierre's syndrome due to Fusobacterium necrophorum

We present a case of a patient with Lemierre's syndrome caused by Fusobacterium necrophorum who developed a right frontal lobe brain abscess. We summarise the epidemiology, microbiology, pathogenesis, clinical presentation, diagnosis, complications, therapy, and outcomes of Lemierre's syndrome. F necrophorum is most commonly associated with Lemierre's syndrome: a septic thrombophlebitis of the internal jugular vein. Patients usually present with an exudative tonsillitis, sore throat, dysphagia, and unilateral neck pain. Diagnosis of septic thrombophlebitis is best confirmed by obtaining a CT scan of the neck with contrast. Complications of the disease include bacteraemia with septic abscesses to the lungs, joints, liver, peritoneum, kidneys, and brain. Treatment should include a prolonged course of intravenous beta-lactam antibiotic plus metronidazole.

Environmental conditions modulate neurotoxic effects of psychomotor stimulant drugs of abuse

Psychomotor stimulants such as methamphetamine (METH), amphetamine, and 3,4-metylenedioxymethamphetamine (MDMA or ecstasy) are potent addictive drugs. While it is known that their abuse could result in adverse health complications, including neurotoxicity, both the environmental conditions and activity states associated with their intake could strongly enhance drug toxicity, often resulting in life-threatening health complications. In this review, we analyze results of animal experiments that suggest that even moderate increases in environmental temperatures and physiological activation, the conditions typical of human raves parties, dramatically potentiate brain hyperthermic effects of METH and MDMA. We demonstrate that METH also induces breakdown of the blood-brain barrier, acute glial activation, brain edema, and structural abnormalities of various subtypes of brain cells; these effects are also strongly enhanced when the drug is used at moderately warm environmental conditions. We consider the mechanisms underlying environmental modulation of acute drug neurotoxicity and focus on the role of brain temperature, a critical homeostatic parameter that could be affected by metabolism-enhancing drugs and environmental conditions and affect neural activity and functions.

Transorbital penetrating injury: case series, review of the literature, and proposed management algorithm

Transorbital penetrating injury (TPI), an uncommon subset of head trauma, requires prompt multidisciplinary surgical intervention. While numerous case reports appear in the literature, there is a lack of discrete recommendations for initial evaluation, surgical intervention, and postoperative care of patients with TPI.

A retrospective review of 4 cases of TPI at the University of Michigan Health System was undertaken to assess for diagnosis, treatment, and follow-up. In addition, a PubMed search using the terms “penetrating orbital trauma,” “penetrating orbital injury,” “transorbital penetration,” and “transorbital penetrating injury” were used to search for articles discussing the presentation and management of penetrating orbital trauma.

All 4 of the patients at the University of Michigan underwent focused physical examination performed by a multidisciplinary trauma team followed by dedicated maxillofacial and head CT scanning. The patients' treatments varied, depending on the mechanism and extent of the injury. An analysis of the case series presented here as well as other published cases suggests an algorithm for diagnosis and treatment for patients with TPI, which includes focused evaluation, diagnostic imaging with maxillofacial CT scanning, and management of the injury that focuses on the path of penetration and the presence of the foreign body in situ at the time of presentation. Magnetic resonance imaging is indicated in patients who have indwelling wooden foreign bodies. Angiography should be performed in patients with suspected vascular injury. Treatment decisions should be made by a multidisciplinary team with input from neurosurgery, ophthalmology, otolaryngology, and maxillofacial surgery.

Improving the role of intraventricular antimicrobial agents in the management of meningitis

PURPOSE OF REVIEW

The aim is to review the role of intraventricular administration of antimicrobial agents in the treatment of patients with bacterial and fungal meningitis.

RECENT FINDINGS

This article discusses indications for intraventricular antimicrobial agents, choice of antibiotics, strategies to monitor pharmacokinetics of central nervous system compartments and unanswered issues for this management approach.

SUMMARY

Intraventricular administration of antimicrobials may be necessary in certain difficult- to- eradicate central nervous system infections. There is a significant need for clinical trials and management guidelines in this area.

Pharmacokinetics, tissue distribution and mass balance of radiolabeled dihydroartemisinin in male rats

BACKGROUND

Dihydroartemisinin (DHA), a powerful anti-malarial drug, has been used as monotherapy and artemisinin-based combination therapy (ACT) for more than decades. So far, however, the tissue distribution and metabolic profile of DHA data are not available from animal and humans.

METHODS

Pharmacokinetics, tissue distribution, mass balance, and elimination of [14C] DHA have been studieded in rats following a single intravenous administration. Protein binding was performed with rat and human plasma. Drug concentrations were obtained up to 192 hr from measurements of total radioactivity and drug concentration to determine the contribution by the parent and metabolites to the total dose of drug injected from whole blood, plasma, urine and faecal samples.

RESULTS

Drug was widely distributed after 1 hr and rapidly declined at 24 hr in all tissues except spleen until 96 hrs. Only 0.81% of the total radioactivity was detected in rat brain tissue. DHA revealed a high binding capacity with both rat and human plasma proteins (76-82%). The concentration of total radioactivity in the plasma fraction was less than 25% of that in blood total. Metabolism of DHA was observed with high excretion via bile into intestines and approximately 89-95% dose of all conjugations were accounted for in blood, urine and faeces. However, the majority of elimination of [14C] DHA was through urinary excretion (52% dose). The mean terminal half-lives of plasma and blood radioactivity (75.57-122.13 h) were significantly prolonged compared with that of unchanged DHA (1.03 h).

CONCLUSION

In rat brain, the total concentration of [14C] was 2-fold higher than that in plasma, indicating the radioactivity could easily penetrate the brain-blood barrier. Total radioactivity distributed in RBC was about three- to four-fold higher than that in plasma, suggesting that the powerful anti-malarial potency of DHA in the treatment of blood stage malaria may relate to the high RBC binding. Biliary excretion and multiple concentration peaks of DHA have been demonstrated with high urinary excretion due to a most likely drug re-absorption in the intestines (enterohepatic circulation). The long lasting metabolites of DHA (> 192 hr) in the rats may be also related to the enterohepatic circulation.

Update in the diagnosis and management of central nervous system infections

Central nervous system (CNS) infections presenting to the emergency room include meningitis, encephalitis, brain and spinal epidural abscess, subdural empyema, and ventriculitis. These conditions often require admission to an intensive care unit (ICU) and are complications of ICU patients with neurologic injury, contributing significantly to morbidity and mortality. Reducing morbidity and mortality is critically dependent on rapid diagnosis and, perhaps more importantly, on the timely initiation of appropriate antimicrobial therapy. New insights into the role of inflammation and the immune response in CNS infections have contributed to development of new diagnostic strategies using markers of inflammation, and to the study of agents with focused immunomodulatory activity, which may lead to further adjunctive therapy in human disease.

Emergency department management of meningitis and encephalitis

Bacterial meningitis and viral encephalitis are infectious disease emergencies that can cause significant patient morbidity and mortality. Clinicians use epidemiologic, historical, and physical examination findings to identify patients at risk for these infections, and central nervous system (CNS) imaging and lumbar puncture (LP) may be needed to further evaluate for these diagnoses. The diagnosis of bacterial meningitis can be challenging, as patients often lack some of the characteristic findings of this disease with presentations that overlap with more common disorders seen in the emergency department. This article addresses considerations in clinical evaluation, need for CNS imaging before LP, interpretation of cerebrospinal fluid results, standards for and effects of timely antibiotic administration, and recommendations for specific antimicrobial therapy and corticosteroids.

Pharmacologic options for CNS infections caused by resistant Gram-positive organisms

Infectious disease continues to evolve, presenting new and challenging clinical situations for practitioners. Specific to device-related and neurosurgical-related CNS infections, Gram-positive organisms are of growing concern. Current Infection Disease Society of America guidelines for the treatment of CNS infections offer little direction after conventional therapy, consisting of vancomycin, has failed or the patient has demonstrated intolerance. A review of literature evaluating alternative therapies, specifically linezolid, quinupristin/dalfopristin, daptomycin and tigecycline, will be presented. Interpretations of these data are offered followed by a brief presentation of future therapies, including ortavancin, telavancin, dalbavancin, ceftobiprole and iclaprim, all of which possess potent Gram-positive activity.

The pharmacokinetics and pharmacodynamics of micafungin in experimental hematogenous Candida meningoencephalitis: implications for echinocandin therapy in neonates

BACKGROUND

Hematogenous Candida meningoencephalitis (HCME) is a relatively frequent manifestation of disseminated candidiasis in neonates and is associated with significant mortality and neurodevelopmental abnormalities. The outcome after antifungal therapy is often suboptimal, with few therapeutic options. Limited clinical data suggest that echinocandins may have role to play in the treatment of HCME.

METHODS

We studied the pharmacokinetics and pharmacodynamics of micafungin in a rabbit model of neonatal HCME and bridged the results to neonates by use of population pharmacokinetics and Monte Carlo simulation.

RESULTS

Micafungin exhibited linear plasma pharmacokinetics in the range of 0.25-16 mg/kg. Micafungin penetrated most compartments of the central nervous system (CNS), but only with doses >2 mg/kg. Micafungin was not reliably found in cerebrospinal fluid. With few exceptions, drug penetration into the various CNS subcompartments was not statistically different between infected and noninfected rabbits. A dose-microbiological response relationship was apparent in the brain, and near-maximal effect was apparent with doses of 8 mg/kg. Monte Carlo simulations revealed that near-maximal antifungal effect was attained at human neonatal doses of 12-15 mg/kg.

CONCLUSIONS

These results provide a foundation for clinical trials of micafungin in neonates with HCME and a model for antimicrobial bridging studies from bench to bedside in pediatric patients.

Brain abscess caused by Streptomyces infection following penetration trauma: case report and results of susceptibility analysis of 92 isolates of Streptomyces species submitted to the CDC from 2000 to 2004

The case of a patient who presented with a brain abscess caused by Streptomyces infection following penetrating cerebral trauma with a soil-contaminated object generated an interest in optimizing antimicrobial therapy. Collaboration with the Centers for Disease Control and Prevention led to the analysis of susceptibility data for Streptomyces isolates that suggested that amikacin (100% susceptibility for 92 isolates tested) and linezolid, an oxazolidinone (100% susceptibility for 41 isolates tested), offer reliable activity against all isolates.

Advances in the management of central nervous system infections in the ICU

This chapter focuses on early aggressive management of common infections of the central nervous system that require monitoring in an ICU setting. These include meningitis, encephalitis, brain and epidural abscess, subdural empyema and ventriculitis. It emphasizes priorities in evaluation and management due to increasing morbidity and mortality as a result of failure to appreciate non-specific symptoms or administer timely therapy. The emergence of organisms resistant to penicillin and cephalosporins has also further complicated the early management of bacterial meningitis. Current antimicrobial guidelines are provided along with discussion of new diagnostic and therapeutic strategies and controversial aspects of management.

Emergency diagnosis and treatment of adult meningitis

Despite the existence of antibiotic therapies against acute bacterial meningitis, patients with the disease continue to suffer significant morbidity and mortality in both high and low-income countries. Dilemmas exist for emergency medicine and primary-care providers who need to accurately diagnose patients with bacterial meningitis and then rapidly administer antibiotics and adjunctive therapies for this life-threatening disease. Physical examination may not perform well enough to accurately identify patients with meningitis, and traditionally described lumbar puncture results for viral and bacterial disease cannot always predict bacterial meningitis. Results from recent studies have implications for current treatment guidelines for adults with suspected bacterial meningitis, and it is important that physicians who prescribe the initial doses of antibiotics in an emergency setting are aware of guidelines for antibiotics and adjunctive steroids. We present an overview and discussion of key diagnostic and therapeutic decisions in the emergency evaluation and treatment of adults with suspected bacterial meningitis.

Levels of vancomycin in cerebrospinal fluid of adult patients receiving adjunctive corticosteroids to treat pneumococcal meningitis: a prospective multicenter observational study

BACKGROUND

Evidence from a recent randomized controlled trial suggests that dexamethasone as adjunct therapy in adult pneumococcal meningitis reduces mortality and neurological sequelae. However, adding dexamethasone has the potential to reduce penetration of vancomycin into the cerebrospinal fluid (CSF). We sought to determine concentrations of vancomycin in serum and CSF of patients with suspected or proven pneumococcal meningitis receiving dexamethasone to assess the penetration of vancomycin into the CSF during steroid therapy.

METHODS

In an observational open multicenter study, adult patients admitted to the intensive care unit because of suspected pneumococcal meningitis received recommended treatment for pneumococcal meningitis, comprising intravenous cefotaxime (200 mg per kg of body weight per day), vancomycin (administered as continuous infusion of 60 mg per kg of body weight per day after a loading dose of 15 mg per kg of body weight), and adjunctive therapy with dexamethasone (10 mg every 6 h). Vancomycin levels in CSF were measured on day 2 or day 3 of therapy and were correlated with protein levels in CSF and vancomycin levels in serum (determined at the same time as levels in CSF).

RESULTS

Fourteen patients were included. Thirteen had proven pneumococcal meningitis; 1 patient, initially suspected of having pneumococcal meningitis, was finally determined to have meningitis due to Neisseria meningitidis. Mean levels of vancomycin in serum and CSF were 25.2 and 7.2 mg/L, respectively, and were positively correlated (r=0.6; P=.025). A positive correlation was also found between the ratio of vancomycin in CSF to vancomycin in serum and the level of protein in CSF (r=0.66; P=.01).

CONCLUSIONS

Appropriate concentrations of vancomycin in CSF may be obtained even when concomitant steroids are used. Dexamethasone can, therefore, be used without fear of impeding vancomycin penetration into the CSF of patients with pneumococcal meningitis, provided that vancomycin dosage is adequate. This study is registered at http://www.ClinicalTrials.gov/ (registration number NCT00162578).

HIV pharmacology: barriers to the eradication of HIV from the CNS

Total eradication of HIV-1 is not yet achievable, in part because reservoirs of latent HIV-1 can develop within lymphoid tissue, the testes, and the central nervous system (CNS). The presence of HIV-1 in the CNS is clinically significant because of its association with the development of HIV dementia, which occurs in up to one fifth of untreated patients. This review summarizes current theory regarding HIV-1 infection within the CNS, describes physiologic and pharmacologic factors limiting CNS penetration of antiretroviral drugs used to treat HIV-1 infection, and reviews current treatment of CNS HIV-1 infection and HIV encephalopathy.

Microdialysis

Microdialysis is a probe-based sampling method, which, if linked to analytical devices, allows for the measurement of drug concentration profiles in selected tissues. During the last two decades, microdialysis has become increasingly popular for preclinical and clinical pharmacokinetic studies. The advantage of in vivo microdialysis over traditional methods relates to its ability to continuously sample the unbound drug fraction in the interstitial space fluid (ISF). This is of particular importance because the ISF may be regarded as the actual target compartment for many drugs, e.g. antimicrobial agents or other drugs mediating their action through surface receptors. In contrast, plasma concentrations are increasingly recognised as inadequately predicting tissue drug concentrations and therapeutic success in many patient populations. Thus, the minimally invasive microdialysis technique has evolved into an important tool for the direct assessment of drug concentrations at the site of drug delivery in virtually all tissues. In particular, concentrations of transdermally applied drugs, neurotransmitters, antibacterials, cytotoxic agents, hormones, large molecules such as cytokines and proteins, and many other compounds were described by means of microdialysis. The combined use of microdialysis with non-invasive imaging methods such as positron emission tomography and single photon emission tomography opened the window to exactly explore and describe the fate and pharmacokinetics of a drug in the body. Linking pharmacokinetic data from the ISF to pharmacodynamic information appears to be a straightforward approach to predicting drug action and therapeutic success, and may be used for decision making for adequate drug administration and dosing regimens. Hence, microdialysis is nowadays used in clinical studies to test new drug candidates that are in the pharmaceutical industry drug development pipeline.

Acute Bacterial Meningitis in Children

Despite advances in recent decades in management, including new and effective antimicrobials, children with bacterial meningitis still incur significant morbidity and mortality. Pathophysiologic processes including colonization and migration of the bacteria to blood, seeding of the meninges, and meningeal and brain inflammation have been largely elucidated, but more specific knowledge could lead to new effective therapies. Outside of the neonatal period, the most common causative organisms have been Haemophilus influenzae, Streptococcus pneumoniae, and Neisseria meningitidis. However, conjugate vaccines, especially the H influenzae type b preparation, have contributed significantly to steep declines in the incidence of meningitis. Optimal management consists of rapid diagnosis and administration of bactericidal antibiotics with properties allowing adequate penetration of the inflamed blood-brain barrier. Recently, development of microbial resistance has resulted in changes to recommended empiric antibiotic regimens. Novel therapies are under investigation; however, until controlled trials can be conducted, these therapies cannot be recommended.

Penetration of dihydroartemisinin into cerebrospinal fluid after administration of intravenous artesunate in severe falciparum malaria

Penetration of cerebrospinal fluid (CSF) by artesunate and DHA was assessed in six adults with cerebral or severe malaria. Lumbar punctures were performed on admission and during convalescence, at 15 min (patient 1), 30 min (patient 2), 45 min (patient 3), 60 min (patient 4), 90 min (patient 5), and 120 min (patient 6) after intravenous administration of 120 mg of artesunate. No artesunate was detectable in CSF. In both studies, DHA levels in CSF increased with time while dihydroartemisinin levels in plasma fell. Dihydroartemisinin might accumulate in CSF during frequent artesunate dosing.

Interactions among strategies associated with bacterial infection: pathogenicity, epidemicity, and antibiotic resistance

Infections have been the major cause of disease throughout the history of human populations. With the introduction of antibiotics, it was thought that this problem should disappear. However, bacteria have been able to evolve to become antibiotic resistant. Nowadays, a proficient pathogen must be virulent, epidemic, and resistant to antibiotics. Analysis of the interplay among these features of bacterial populations is needed to predict the future of infectious diseases. In this regard, we have reviewed the genetic linkage of antibiotic resistance and bacterial virulence in the same genetic determinants as well as the cross talk between antibiotic resistance and virulence regulatory circuits with the aim of understanding the effect of acquisition of resistance on bacterial virulence. We also discuss the possibility that antibiotic resistance and bacterial virulence might prevail as linked phenotypes in the future. The novel situation brought about by the worldwide use of antibiotics is undoubtedly changing bacterial populations. These changes might alter the properties of not only bacterial pathogens, but also the normal host microbiota. The evolutionary consequences of the release of antibiotics into the environment are largely unknown, but most probably restoration of the microbiota from the preantibiotic era is beyond our current abilities.

Enantioselective distribution of albendazole metabolites in cerebrospinal fluid of patients with neurocysticercosis

AIMS

Albendazole (ABZ) is effective in the treatment of neurocysticercosis. ABZ undergoes extensive metabolism to (+) and (-)-albendazole sulphoxide (ASOX), which are further metabolized to albendazole sulphone (ASON). We have investigated the distribution of (+)-ASOX (-)-ASOX, and ASON in cerebrospinal fluid (CSF) of patients with neurocysticercosis.

METHODS

Twelve patients with a diagnosis of active brain parenchymal neurocysticercosis treated with albendazole for 8 days (15 mg kg(-1) day(-1)) were investigated. On day 8, serial blood samples were collected during the dose interval (0-12 h) and one CSF sample was taken from each patient by lumbar puncture at different time points up to 12 h after the last albendazole dose. Albendazole metabolites were determined in CSF and plasma samples by h.p.l.c. using a Chiralpak AD column and fluorescence detection. Population curves for CSF albendazole metabolite concentration vs time were constructed.

RESULTS

The mean plasma/CSF ratios were 2.6 (95% CI: 1.9, 3.3) for (+)-ASOX and 2.7 (95% CI: 1.8, 3.7) for (-)-ASOX, with the two-tailed P value of 0.9873 being non-significant. These data indicate that the transport of ASOX through the blood-brain barrier is not enantioselective, but rather depends on passive diffusion. The present results suggest the accumulation of the (+)-ASOX metabolite in the CSF of patients with neurocysticercosis. The CSF AUC(+)/AUC(-) ratio was 3.4 for patients receiving albendazole every 12 h. The elimination half-life of both ASOX enantiomers in CSF was 2.5 h. ASOX was the predominant metabolite in the CSF compared with ASON; the CSF AUC(ASOX)/AUC(ASON) ratio was approximately 20 and the elimination half-life of ASON in CSF was 2.6 h.

CONCLUSIONS

We have demonstrated accumulation of the (+)-ASOX metabolite in CSF, which was about three times greater than the (-) antipode. ASOX concentrations were approximately 20 times higher than those observed for the ASON metabolite.

Central Nervous System Infections in the Immune-competent Adult

The clinician must maintain a high level of suspicion for central nervous system infections even if not all of the classic signs are present, because prompt treatment may make a difference in patient outcome. If bacterial meningitis is suspected, a CT scan of the head should be obtained prior to lumbar puncture if there is papilledema, a focal neurologic exam, or if the patient is comatose. In bacterial meningitis, empiric antibiotics should be chosen based on a patient's risk factors and should be started immediately. Depending on the resistance patterns of the institution, Streptococcus pneumoniae may be resistant to penicillins and cephalosporins. Corticosteroids are of uncertain benefit in bacterial meningitis and may decrease the penetration of antibiotics into the central nervous system. The dosage for acyclovir treatment in herpes simplex encephalitis is 10 to 15mg/kg every 8 hours. Subdural empyema is a neurosurgical emergency. Brain abscesses should be surgically drained if they exceed 2.5 centimeters.

Structure of the protease domain of memapsin 2 (beta-secretase) complexed with inhibitor

Memapsin 2 (beta-secretase) is a membrane-associated aspartic protease involved in the production of beta-amyloid peptide in Alzheimer's disease and is a major target for drug design. We determined the crystal structure of the protease domain of human memapsin 2 complexed to an eight-residue inhibitor at 1.9 angstrom resolution. The active site of memapsin 2 is more open and less hydrophobic than that of other human aspartic proteases. The subsite locations from S4 to S2' are well defined. A kink of the inhibitor chain at P2' and the change of chain direction of P3' and P4' may be mimicked to provide inhibitor selectivity.